(1) Field of Invention
This invention relates to a hole enlargement arrangement and method of use; more specifically to an underreamer that provides a cutter arm assembly supported, upon extension, by a slideable, non-pivoting stop block which passes all shocks absorbed by the cutter arm to the outer body of the tool.
(2) Description of Related Art including information disclosed under 37 CFR 1.97 and 1.98
Various types of hole enlargement arrangements have been heretofore employed and are currently in use. In the devices with which applicant is familiar, a body structure formed of inner and outer body sections has cutter arms pivotally secured on the outer body section and a piston and cylinder means defined between the inner and outer body sections receives hydraulic fluid to effect telescopic movement of the body sections in one relative direction whereupon a cam surface mechanically engages and forces cutter arms out to an underreaming or bore hole enlarging position. This arrangement is more clearly shown in U.S. Pat. No. 4,614,242, which is incorporated herein by reference as background information for this application.
After the underreaming operation is completed, the cutter arms of the prior art devices are generally then retracted by reducing the pump pressure and raising the operating string on which the body structure is supported so that the expanded or projecting arms engage the shoulder formed at the point of commencement of the underreaming. Continued raising of the operating string exerts a force on the extended cutter arms to move the arms inwardly to a retracted position relative to the body structure.
When the arms of the underreamer are extended during hole enlarging operations to underream or drill an enlarged portion in a bore hole, there are various forces that act upon the cutter arms, such as an upwardly directed force on the outer projecting end of the arm due to the weight of the operating string during underreaming reacting with the well bore.
In the prior art devices, these forces are transmitted from the cutter arms to the pivot arrangement of the cutter arms on the body structure and to the cam surface which is relied upon to move and maintain the cutter arms in an extended cutting position, then to the yoke and threads connecting the inner tube elements. These forces may be substantial and, in some instances, repeated use will damage or break components of the underreamer where the inner body was threaded to the yoke assembly. Wear from continued use of the device causes vibration of the arm and underreamer in extension, causing or accelerating further wear, damage or failure of these types of tools.
The present invention provides an arrangement that assists in overcoming the above problems by transferring all mechanical forces acting on the cutter arm to the slideable, non-pivoting stop block and the outer body. The solidity of the stop block seated against the outer body of the underreamer also provides additional strength to deformation from the lateral forces acting upon the underreamer in contact with the well bore. As an additional benefit, the improved underreamer arm assembly can retrofit an existing underreamer body with these new components.
The inner body structure and a cooperative support arrangement move the stop block and arms into position on the outer body section. This cooperative support to yoke arrangement moves the cutter arms to the extended cutter position. The cooperating support arrangement is relieved of supporting the extended arms. Because the stop block and outer body fully support and assist in distributing the loads and forces employed during the bore hole enlarging operation, the support provided by the stop block and outer body also increase the mechanical advantage tending to maintain the cutter arms in an expanded position during underreaming. The shape of the stop block accommodates a full metal-to-metal contact between the base of the cutter arm and outer body and thereby avoids passing these large shock loads on to the threaded or weaker internal components of the underreamer device.